y = previous(x,init);
The previous function delays the input signal x and holds it for one sample interval. It is equivalent to the z-1 discrete time operator.
x = sin(time*0.3);
y = sample(x);
z = previous(y);
u = hold(z);
x and y will become discrete signals. 20-sim will automatically detect the existence of discrete signals. Each chain of discrete signalswill be assigned a specific sampletime. You can set this sample time to any desired value in the Simulator (choose Properties, Simulation and Discrete System).